[FPSPACE] FW: NEO News (04-17-06) Dawn, Planetary Defense, Comets

[LARRY KLAES]

>From: David Morrison <dmorrison at arc.nasa.gov>
>To: David Morrison <dmorrison at arc.nasa.gov>
>Subject: NEO News (04-17-06) Dawn, Planetary Defense, Comets
>Date: Mon, 17 Apr 2006 17:29:19 -0700
>
>
>NEO News (04-17-06) Dawn, Planetary Defense, Comets
>
>Following are three stories, one announcing the next Planetary Defense 
>Conference (March 2007) and the other two stories dealing with new ideas on 
>the nature of comets. First, however, the good news of the reinstatement of 
>the Dawn Discovery mission, which will orbit the largest main-belt 
>asteroids, Ceres and Vesta. On 1 March we reported that NASA had decided on 
>the "indefinite postponement" of this mission, and a few days later NASA 
>announced its cancellation. However, a formal cancellation review 
>subsequently gave the mission a clean bill of health, concluding that major 
>technical difficulties seemed to have been overcome, and therefore NASA has 
>decided to continue with the mission.
>
>David Morrison
>
>====================
>
>2007 PLANETARY DEFENSE CONFERENCE: CALL FOR PAPERS
>
>5-8 March 2007
>George Washington University
>Washington, D.C.
>
>Papers are now being solicited for the 2007 Planetary Defense Conference. 
>To download a copy of the Call for Papers, go to 
><http://www.aero.org/conferences/planetarydefense/cfp.pdf>. This conference 
>will consider planetary protection from the systems prospective and cover 
>the following areas:
>
>* Detect and define the threats
>* Look at deflection options and available technologies
>* Examine recent missions with an eye towards lessons learned for 
>deflection missions
>* Discuss characteristics of candidate missions to mitigate the threats
>* Consider the policy and disaster preparedness implications.
>
>Participants will develop a set of recommended actions to improve our 
>ability to successfully defend Earth from possible impacts.
>
>This is the second Planetary Defense Conference and will be repeated every 
>several years to assess progress, incorporate new technology and provide an 
>ongoing focus to this important work.
>
>Depending on funds available, a limited number of honoraria will be awarded 
>to invited speakers. To encourage student participation, a limited number 
>of scholarships will be awarded to students whose papers are judged by the 
>steering committee as being particularly relevant to the conference goals 
>and focus areas.
>
>A goal of the conference is to focus on technologies, capabilities, and 
>issues that in the next 15 years are likely to affect the decision to 
>undertake a deflection mission, to enable a deflection, to prepare the 
>public for a deflection effort, or to respond to an impact-related 
>disaster. Authors should keep this in mind as they prepare their abstracts 
>and papers.
>
>Abstract Submittal
>
>Technical paper abstracts (no less than 500 words in length and in pdf 
>format) will be accepted electronically at <asteroid at aero.org> beginning 2 
>March 2006. Please be sure to designate to which topic area your paper 
>correlates. Papers dealing with education and design in the identified 
>categories, as well as international collaboration projects, are invited 
>and encouraged. Abstracts may include key figures and references to 
>pertinent publications in existing literature.
>
>Accepted papers will be published on the conference Web site and will be 
>included on the conference CD-ROM. Most speakers at the conference will be 
>invited, but a limited number of submitted papers may be selected for 
>presentation. The remainder of accepted papers will be posters. Authors of 
>all poster papers will be able to present a two-minute, two-slide 
>presentation during the regular session. With their final manuscripts, 
>authors must include a cover letter that indicates they have received the 
>appropriate company and/or sponsoring agency approval for public release. 
>The format for papers will be provided on the conference Web site at a 
>later date.
>
>The deadline for receipt of abstracts via electronic submission is 13 
>October 2006. Technical program chairs will notify authors of conditional 
>acceptance or rejection on or before 3 November 2006. Letters of official 
>acceptance and instructions will be mailed on or before 10 November 2006. 
>The deadline for submission of the final written paper is 16 February 2007.
>
>The 2007 Planetary Defense Conference is sponsored by:
>
>The American Institute of Aeronautics and Astronautics (AIAA)
>The Aerospace Corporation
>Space Studies Institute (SSI)
>SpaceWorks Engineering, Inc.
>
>====================
>
>CLANDESTINE COMETS FOUND IN MAIN ASTEROID BELT
>
>23 March 2006
>NewScientist.com news service
>Kimm Groshong
>
>You do not have to look to the outer edges of the solar system, or even out 
>beyond Neptune to observe a reservoir of comets. A bevy of the 
>ice-containing bodies lies disguised as main-belt asteroids between Mars 
>and Jupiter, claim astronomers from the University of Hawaii, US.
>
>David Jewitt and Henry Hsieh have dubbed the new population "main belt 
>comets". They describe three objects with near circular, flat orbits in the 
>asteroid belt that stream volatile materials, producing an observable tail 
>for weeks and months at a time.
>
>The finding backs a theory that ice-bearing asteroids - or "comets" - from 
>this much closer region may have played an important role in forming the 
>Earth's oceans.
>
>Scientists once believed the icy comets from the outer regions of the solar 
>system were the most likely source of the water that transformed the early 
>Earth from a dry, barren world. But chemical analyses of comet water - 
>carried out from a distance - ruled out the possibility.
>
>Another possibility was asteroids. But it had seemed impossible to study 
>the water content of asteroids since most of their water appears to have 
>dissipated or is now buried too deeply to observe.
>
>Now Jewitt says this new population within the asteroid belt may provide a 
>way to sample the chemicals in water on or near the surface of these 
>objects. And he says the main-belt comets hold promise for future study as 
>components of the protoplanetary disc that surrounded the Sun - the disc 
>from which the planets formed. "They're a window to some early epoch, back 
>when objects were accreting," he says.
>
>The new study underscores the increasingly hazy distinction between comets 
>and asteroids. "There are different definitions of comet used by different 
>people at different times," Jewitt told New Scientist.
>
>The two traditionally recognised comet reservoirs are the Kuiper Belt, a 
>frigid region beyond Neptune's orbit, and the even more distant Oort Cloud. 
>One definition describes a comet as an object following a highly 
>elliptical, often inclined orbit with origins in one of these two 
>reservoirs.
>Carbonaceous covering
>
>But another definition involves what an observer sees either with the naked 
>eye or through a telescope - a comet's streaming gassy tail as it loses ice 
>and other volatile materials through being warmed by the Sun.
>
>Jewitt says based on their nearly circular, stable orbits, the main belt 
>comets are "completely asteroidal". You would never guess that they were 
>anything but asteroids." But in terms of appearance, with their 
>long-lasting tails, he says "they're definitely comets".
>
>The team believes in order to survive at such proximity to the Sun, the 
>volatiles in the main belt comets would have to be covered by a layer of 
>possibly carbonaceous material. They say an impact event could then uncover 
>some of the volatiles, allowing the Sun's heat to trigger the observed 
>outgassing.
>Activated asteroids
>
>Asteroid expert Richard Binzel at MIT questions the need for the new 
>classification. "I prefer to think of them as activated asteroids," he told 
>New Scientist. "It's no surprise if some asteroids have some water content, 
>particularly in the outer asteroid belt."
>
>He says volatiles have been measured to make up about 10% of some 
>carbonaceous meteorites that are thought to come from the region.
>
>Jewitt says potentially tens of thousands of main belt objects contain ice 
>and have simply not been observed during their active period. In order to 
>be seen spewing dust, the objects would have to have been hit by a meteor 
>size boulder within the last thousand years or so, he adds.
>
>Journal reference: Science (DOI: 10.1126/science.1125150)
>
>===========================
>
>THE COMETS' TALE: MAYBE THE DIRTY SNOWBALL THEORY IS WRONG
>
>by David L. Chandler
>The Boston Globe
>April 10, 2006
>
>Three fly-by missions since 2001 have confounded almost everything 
>astronomers thought they knew about the makeup of comets. Then, two weeks 
>ago, University of Hawaii researchers announced the discovery of a whole 
>new family of close-in comets -- which might help explain how the early 
>Earth got its water.
>
>Our lack of knowledge could have dire consequences, scientists warn, 
>because -- unlike asteroids, whose paths can be predicted years in advance 
>-- comets could strike Earth with little warning. The missions have proven 
>that we don't know enough about these dazzling lumps of ice and dirt to 
>know how to respond.
>
>But now, one astronomer has come up with a theory that might tie some of 
>the loose ends together. Instead of the conventional view of a comet's 
>nucleus as a solid, several-miles-wide rubble pile or dirty snowball, 
>Michael Belton, a lead scientist for last year's Deep Impact comet mission, 
>suggests that the nucleus may be more like a lump of papier mache -- built 
>up from a random assortment of irregular sheets of varying thickness.
>
>''The presence of layers is ubiquitous" in the nuclei seen so far, Belton 
>said, ''and may be an essential element of their internal structure." In 
>his view, the nuclei were built up gradually as hundreds of smaller bodies 
>smashed together over time, each flattening out and sticking to the growing 
>body, forming one layer after another.
>
>Astronomers were startled and confused by the dramatic and unexpected 
>differences between the nuclei of Tempel 1 (seen by last year's Deep Impact 
>mission), Wild 2 (as seen by the Stardust mission in 2004) and Borrelly 
>(seen by deep Space 1 in 2001).
>
>Belton's new theory, which he outlined at a conference in Houston last 
>month, identifies all the varied and unexplained features seen on these 
>comets -- including supposed craters on Wild 2, mesa-like plateaus on 
>Borrelly, and distinctly different, overlapping surface textures on Tempel 
>1 -- as different aspects of the layered model he nicknamed Talps (for 
>''splat" spelled backwards).
>
>Clark Chapman, a specialist in asteroids and comets at the Southwest 
>Research Institute in Boulder, Colo., agrees with Belton that ''it looks 
>like comets have layers in them," but he said the theory is still untested. 
>''It's a first step toward trying to understand comets differently."
>
>The new model would have significant implications for the life cycle of 
>comets and for how we might attack a comet headed for Earth. Pushing aside 
>a solid ball with a huge rocket or nuclear blast might make sense, but 
>using the same approach against a ball of many layers might cause the comet 
>to splinter and could magnify the damage rather than avert it, Belton 
>suggests.
>
>The find of a new type of comet -- the third known -- adds a lot of new 
>questions to comet research and possibly helps answer a longstanding 
>mystery: How the Earth has so much water when models suggest it shouldn't.
>
>As the solar system's inner planets coalesced from the cloud of gas and 
>dust swirling around the sun, the sun's heat caused water to evaporate. The 
>new discovery suggests that Earth's water supply might have been 
>replenished by some comets or asteroids that initially formed just a bit 
>farther out and so might have retained their ice as they hurtled around the 
>sun and eventually smashed into our planet.
>
>Astronomers Henry Hsieh and David Jewitt of the University of Hawaii 
>announced late last month that they have found comets with asteroid-like 
>orbits -- circling the sun as planets do, between Mars and Jupiter, instead 
>of the very elongated orbits characteristic of all previously known comets. 
>Finding comets like these suggests that there could be icy asteroids or 
>comets that formed much closer to the sun than previously thought. They 
>would have replenished Earth's water supply when they crashed into its 
>surface.
>
>''I think it's very significant," Jewitt said, to find such a fundamentally 
>different group of comets, which must have formed separately from all the 
>others. But it will take more study to figure out how this new population 
>will compare to the others and what kind of structure they might have. 
>Being born in a hotter region of the growing solar system, for example, 
>might have produced a different kind of layering, if any.
>
>Belton, president of Belton Space Exploration Initiatives in Tucson, said 
>he'd like to have a chance to prove his model by getting a closer look at 
>some of these comets, particularly with a radar analysis -- which past 
>missions couldn't perform -- that could clearly show whether the orb is 
>layered deep down.
>
>It may be a while before he gets that wish, but the European Space Agency's 
>Rosetta mission will provide close-up views in 2014 of another comet 
>nucleus and will use microwaves to probe its inner structure. Other comet 
>missions have been proposed. ''The reconnaissance is over," Belton said. 
>''It's time to get into the detailed exploration phase."
>
>--
>+++++++++++++++++++++++++++++++++++++++++++
>
>NEO News (now starting its second decade of distribution) is an informal 
>compilation of news and opinion dealing with Near Earth Objects (NEOs) and 
>their impacts. These opinions are the responsibility of the individual 
>authors and do not represent the positions of NASA, the International 
>Astronomical Union, or any other organization. To subscribe (or 
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>please see the website http://impact.arc.nasa.gov. If anyone wishes to copy 
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>please include this disclaimer.